Powder coatings utilize pulverized polyester, epoxy or polyurethane plastics, extruded and ground to specific particle size ranges depending on the painting application. The powders are preferably thermoset or thermoplastic polymers with additives and pigments. Powder materials have the consistency of talc or flour and pose no environmental hazards, and pose the same health risks as any air born dust.
Powder coating guns are used to apply protective coatings on industrial and commercial products. In summary, the powder coating process is as follows. A powder gun is provided with a step-up transformer to supply high voltage power to an emitter located in the outlet nozzle of the powder coating gun. Present powder coating guns are also provided with a source of compressed air that flows through a container containing the powder coating. The container is usually an external jar or appendage to the guns. The source of compressed air for present powder coating guns is an external air compressor or compressed air source such as a tank which is attached to the gun through an air hose. The air hose most often used to provide existing guns with compressed air is the type used to supply compressed air to a variety of air powered tools and connect to a typical gun with commonly used air hose fittings and connectors.
The compressed air introduced into powder coating guns entrains the powder coating, the coating then being fluidized, and is passed parallel to an emitter which imparts an electrical charge to the powder coating material. The charged coating powder is thereafter sprayed in the direction of the grounded work piece to be coated. The work to be sprayed being at ground potential, from an electrical charge perspective, the charged coating powder is attracted to and deposits uniformly on the surface of the grounded work piece.
After the work piece has been coated with the powder coating, the work piece is cured in an oven at approximately 400° F. for 10 minutes. The deposited powder melts and flows together to bond and form a more permanently adhered coating on the work piece as it cools.
Conventional solvent based paint technology has several disadvantages. Spills from paint containing inorganic solvents pose a threat to the environment. Millions of aerosol paint cans are sold each year and contribute to environmental destruction and land fill concerns. The propellants and volatile organic compounds given off by aerosol paints are very toxic to both the user and bystanders. The over spray is also a concern when aerosol paints are used.
Powder coating technology has a number of advantages over conventional solvent-based paint technology. Powder coating is an environment friendly solution as the level of accidental spills are reduced, and the content of the spill is a particulate dust that can be easily collected and disposed. Also, powder coating technology enables the application of a uniformly thick coating and automated operation. Powder coatings also show excellent chemical resistance to gasoline, oil, methyl ethyl ketone, acetone and household cleaners. Powder coatings are also more flexible than conventional solvent based paints. Powder coatings are also ultra violet resistant, and maintain high gloss and luster for years in outdoor exposure.
Powder coatings are used to coat a variety of products such as automotive components, metal office furniture and storage shelving, electrical transformers, and recreational equipment. Present powder coating systems are not well adapted for use by the casual users, hobbyist, or any application in which the user does not have an air compressor and a dedicated paint preparation area to facilitate cleaning the paint gun throughly each time a color change is desired with the same powder coating gun.
The primary components of a powder coating system is the powder coating gun, supply and control of the air required to entrain the powder coating materials, and a supply of high voltage power to an electrode referred in the trade and in this application hereafter as an emitter. High voltage is required to charge the emitter located in or near the discharge nozzle of the powder coating gun to produce a corona effect that imparts an electrostatic charge to the powder coating particles that pass through the ionizing field at the tip of the emitter, and which are subsequently directed towards the work piece to be painted. As the entrained powder coating material passes through this ionizing field of the air space at tip of the emitter, the powder particles are charged and drawn to the grounded work piece to be painted.
Currently, powder coating work is undertaken primarily by manufacturers and custom coaters. The equipment used to apply the powder coating ranges in price from $1,000 to $25,000 and ovens used for curing are typically large in size. Manufactures hang the products to be coated from large overhead conveyors and apply powder either manually or with robotic “gun movers”. Once the powder is applied to the product, the product is placed in large gas or electric ovens that cure the powder at about 400° F. for approximately 10 minutes at peak metal temperature. The curing process is very important. Curing temperatures or an oven residence time below the optimum will result in under-cured powder, which may chip easily when the product is put in service.
As described above, conventional powder coating systems use an air compressor located external to the body of the powder coating gun to supply pressurized air to entrain or fluidize the powder coating material. The flow rate of the compressed air is controlled by regulators in a control panel external to the powder coating gun itself. The flow rate of the air is proportional to the rate of utilization of the powder coating material. When a fine powder coating is used, an over-supply of compressed air reduces the coating powder usage efficiency.
In conventional powder coating gun systems, the powder coating flow path within the powder coating gun generally requires cleaning when the powder coating or the powder color is changed. This coating powder build-up is more significant at the outlet section of the coating powder flow path including the discharge nozzle of the powder coating gun and powder feed hose or line. In general, the nozzle and feed hose need to be cleaned when ever the powder color is changed. Cleaning the gun is a time consuming process for the operator.
Industrial guns charge the particles at voltages of approximately 80,000 volts. Use of such high voltages is a safety risk in non-commercial and household applications. Industrial guns and other present art systems require a source of compressed air externally to provide the air flow necessary to operate such tools. The home craftsman, hobbyist or small shop owner is not well served by the features or requirements of the present art in powder coating systems for such reasons. A self contained tool which eliminates the need for an air compressor and elaborate shop facilities for cleaning the gun between uses is needed.
Accordingly, there is an unsatisfied need for a powder coating gun that allows a quick-change of paint cartridges, obviates the need for an external air compressor, and runs at a lower and safer voltage to enable use of the powder coating powder gun system in non-commercial and home applications.